1. Field of Invention
This invention generally relates to light engines for image display projectors
2. Prior Art
The separation of light into usable colors is a critical function incorporated into projector light engines. Various technologies, such as the sequential color wheels, prism systems, etc., have been developed for such separation of colors from full visible spectrum or “white” light. Color wheels are particular to reflective image generation devices (“imagers”) such as DLP manufactured by Texas Instruments Corp. and may also used in some LCOS systems available from various suppliers. The light source for projection systems is generally broad spectrum (“white light”) sources such as high intensity discharge (“HID”) lamps manufactured by Philips and others. These lamps are typically use 75 to 150 watts power and provide adequate light for projection but are generally inefficient, light quality degrades over time, extensive cooling is required and HID lamps have lifetime limitations. An emerging technology is the use of light emitting diodes (“LED”), which are solid-state laser light sources. They can be monochromatic and can be pulsed. Table 1 is a description of typical design requirements for an LED light source as incorporated into a light engine. Ideally at least three separate, monochromatic LED's, usually in red, blue and green, would be used. Each respective color is turned on and off at a frequency of 3 to 5 KHz. LED light sources are limited by the total lumens generated per color and the relatively large size of the emitting region (etendue) required. LED's can be long lived but are generally low efficiency and generate significant beat that must be removed.
TABLE 1CURRENT DESIGN TARGETS FOR LED LIGHT SOURCESParameterTargetComments2/07 Add'l Comments CDTotal Flux(180° Output)Assume duty cycle <60%Very dependent on sourceBrightnessRed: ~425 averageper color that may beetendue, imager size, screenlumensadjusted randomly.size and gain. Imager isGreen: ~1500 averageAssuming >70%currently 0.65″ diagonallumenscollected in 60moving to 0.45″ diagonal inBlue: ~130 averagedegree conesize. Ultimate target islumens1000 nits on screen with 2×gain.LED~12 mm{circumflex over ( )}2 for 0.65″Imaged onto a 16:9 deviceEmittingimagerilluminated at ~28° atAreaapprox. f/2.0 × f/2.4Junction to□ 1 C/WTotal heat dissipationCasecapability of systemThermalheatsink solution isResistancetypically ~.5 C/W duringoperationOperating2-5 KHzTypical pulsing rate duringWith color sequentialFrequencyoperation (per color)system, switching speed 10is ~2800 Hz.uS (full off to full on) andpulse periods down to 400uS.Operating1%-60%May be adjusted randomlyPer color per frameDuty Cycle(per color)VariabilityOperating10-45 C.Typical conditions - variesAmbientby OEM product designTemperaturerequirementsRangeOperatingMinimum: 20,000 HrsTarget 60K hours asLifetimeTypical: 60,000 HrsminimumOperating0%-100%Operating current may varyCurrentrandomly - OhmicVariabilityResistance must be lowenough to support stableturn on at low current levelsDieRotation: TBDplacementX/Y: TBDtolerance topackagealignmentfeaturesTargetRed: ~620-630 nmNominal OutputOutputGreen: ~520-540 nmWavelengths (per color)WavelengthsBlue: ~455-465 nmutilizing the bestcombination of wavelength,duty cycle, and intensity formaximum brightness
3. Objectives
This invention is a method and apparatus for producing a light engine with three separate monochromatic light sources, typically red, blue and green, combined into one light generation device powered by microwaves pulsed at 3-5 KHz rates. The individual light sources are cylindrical or spherical in shape with internal dimensions in any direction generally less than 0.6 mm. They would generally generate power densities exceeding 15,000 watt/cm3.